A conventional process of manufacturing a large area semiconductor element applies the technique of injecting impurities into a semiconductor thin film etc. An example of this method comprises the steps of:
(1) discharge-decomposing a gas containing impurities for controlling valence electrons such as hydrogen diluted with phosphine (PH.sub.3);
(2) driving produced ions without mass-separating them as a wide aperture ion beam into a semiconductor thin film to form a doping layer;
(3) subsequently removing the element into the air and forming a metal film in a separate vacuum device; and
(4) patterning, rinsing, and heat treating the metal film, which is then completed as a semiconductor element.
In the above-mentioned conventional method, it is easy to dope a large area.
However, when a doping process takes place, hydrogen ions are injected simultaneously, so due to highly concentrated hydrogen atoms which are present near the surface of the doping layer, the doping layer becomes extremely unstable and active near its surface. In addition, since other processes after the ion irradiation are performed in other devices, samples are exposed to air, which results in forming an oxide film by easily bonding with moisture or oxygen in the air, as shown in FIG. 4 (a). As a result, the characteristics and reliability of the semiconductor element are deteriorated.